In recent years, thermal transfer systems have been developed to obtain prints from pictures that have been generated electronically. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta and yellow signals. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Further details of this process and an apparatus for carrying it out are set forth in U.S. Pat. No. 4,621,271.
Dye-receiving elements used in thermal dye transfer generally comprise a polymeric dye image-receiving layer coated on a support. Supports are required to have, among other properties, adequate strength, dimensional stability, and heat resistance. For reflective viewing, supports are also desired to be as white as possible. Cellulose paper and plastic films have been proposed for use as dye-receiving element supports in efforts to meet these requirements. Recently, microvoided films formed by stretching an orientable polymer containing an incompatible organic or inorganic material have been suggested for use in dye-receiving elements.
Various arrangements have been proposed to improve the imaging quality of dye image receiving layers in thermal dye-transfer elements. JP 88-198,645 suggests the use of a support comprising a polyester matrix with polypropylene particles as a dye donor element. EP 582,750 suggests the use of a non-voided polyester layer on a support.
U.S. Pat. No. 5,100,862 relates to microvoided supports for dye-receiving elements used in thermal dye transfer systems. Polymeric microbeads are used as void initiators in a polymeric matrix to enable higher dye transfer efficiency. A problem exists with such support, however, in that in order to attain the high level of voiding necessary for desired dye transfer efficiency, the volumetric loading of the microbeads needs to be above 25% by volume of the polymeric matrix. The degree of voiding is preferably from about 30 to 60 volume percent. At these levels of loading the tear strength of the film during manufacture is very low and results in very poor manufacturing efficiency due to tearing of the support.
U.S. Pat. No. 6,096,684 relates to porous polyester films suitable as supports for receiving elements used in thermal dye transfer systems. Polymers immiscible with a polyester are used in a base layer while an adjacent layer, upon which a dye receiving layer is formed, contains a polyester containing dispersed inorganic particles as void initiators. These inorganic particles are less than 1.0 μm in size. The porosity of layer (B) is specified to be not less than 20% by volume. This support solves the problem of poor adhesion of imaging layers to a support consisting only of layer (A). This support has also been shown to be manufacturable at high efficiency. A problem exists with this support, however, in that the hardness of the inorganic void initiators results in poor contact with the dye donor element. This results in low dye transfer efficiency for elements using such supports.
This problem was addressed by U.S. application Ser. No. 10/033,481 whereby the inorganic particles of layer (B) in U.S. Pat. No. 6,096,684 are replaced with polymeric microbeads. This significantly improved the dye transfer efficiency. This invention provides a thermal dye-transfer dye-image receiving element comprising a dye-receiving layer 1, a microvoided layer 2, beneath layer 1, containing a continuous phase polyester matrix having dispersed therein crosslinked organic microbeads and having a void volume of at least 25% by volume and, beneath layer 2, a microvoided layer 3 comprised of a continuous phase polyester matrix having dispersed therein non-crosslinked polymer particles that are immiscible with the polyester matrix of layer 3. The invention is said to provide a receiver exhibiting an improved combination of dye-transfer efficiency and tear strength.
It would be desirable to have a dye image-receiving element for thermal dye transfer which exhibits tear-resistance, a high dye transfer efficiency, which is capable of recording images (including color images) having high optical densities, high image quality, and capable of being manufactured at a relatively low cost.